Non-linear spectroscopy of rubidium: An undergraduate experiment

In this paper, we describe two complementary non-linear spectroscopy methods which both allow to achieve Doppler-free spectra of atomic gases. First, saturated absorption spectroscopy is used to investigate the structure of the $5{\rm S}_{1/2}\to 5{\rm P}_{3/2}$ transition in rubidium. Using a slightly modified experimental setup, Doppler-free two-photon absorption spectroscopy is then performed on the $5{\rm S}_{1/2}\to 5{\rm D}_{5/2}$ transition in rubidium, leading to accurate measurements of the hyperfine structure of the $5{\rm D}_{5/2}$ energy level. In addition, electric dipole selection rules of the two-photon transition are investigated, first by modifying the polarization of the excitation laser, and then by measuring two-photon absorption spectra when a magnetic field is applied close to the rubidium vapor. All experiments are performed with the same grating-feedback laser diode, providing an opportunity to compare different high resolution spectroscopy methods using a single experimental setup. Such experiments may acquaint students with quantum mechanics selection rules, atomic spectra and Zeeman effect.Comment: 16 pages, 8 figure

Instability driven fragmentation of nanoscale fractal islands

Formation and evolution of fragmentation instabilities in fractal islands, obtained by deposition of silver clusters on graphite, are studied. The fragmentation dynamics and subsequent relaxation to the equilibrium shapes are controlled by the deposition conditions and cluster composition. Sharing common features with other materials' breakup phenomena, the fragmentation instability is governed by the length-to-width ratio of the fractal arms.Comment: 5 pages, 3 figures, Physical Review Letters in pres

Palaeontological data about the climatic trends from Chattian to present along the Northeastern Atlantic frontage

Climatic changes that affected the Northeastern Atlantic frontage are analyzed on the basis of the evolution of faunas and floras from the late Oligocene onwards. The study deals with calcareous nannoplankton, marine micro- and macrofaunas, some terrestrial vertebrates and vegetal assemblages. The climate, first tropical, underwent a progressive cooling (North-South thermic gradient). Notable climatic deteriorations (withdrawal towards the South or disappearance of taxa indicative of warm climate and appearance of "cold" taxa) are evidenced mainly during the Middle Miocene and the late Pliocene. Faunas and floras of modern pattern have regained, after the Pleistocene glaciations, a new climatic ranging of a temperate type in the northern part

Chapter A4 Sr isotope record in the area of the lower miocene historical stratotypes of the aquitaine basin (France)

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Homogeneous and heterogeneous clustering in the accretion regime

Condensation of nano-droplets in a supersaturating vapor decomposes in two steps: the formation of a nucleation center, also called critical nuclei or nucleation seed, and the growth sequence, by accretion of further atoms on the nucleation center. These two steps have been investigated separately through the clustering of homogeneous particles Nan and heterogeneous particles NanX in a helium buffer gas (X = (Na2O)2 or (NaOH)2). The growth sequence is analyzed with preformed molecules X injected in a supersaturating sodium vapor and driving production of NanX clusters. Cluster distribution mean sizes are controlled by sodium concentration and by the condensation cell effective length. The signal intensities observed for homogeneous and heterogeneous clusters are proportional to the homogeneous and heterogeneous nucleation center numbers respectively. We can measure the efficiency for the homogeneous nucleation center production versus sodium concentration. This process is the onset of the condensation phase transition.

Diffusion of silver nanoparticles on carbonaceous materials. Cluster mobility as a probe for surface characterization

The effect of support geometry and structure on nanoparticles diffusion, nucleation and coalescence was already shown. In this paper, we focus on an alternative use of the interaction between deposited clusters and the substrate for the characterization of surface properties. The use of clusters deposition as probe for surface states characterization appears as an attractive and remarkable tool